In a data network that supports VoIP communications, whether the network is wired or wireless or a combination of the two, the location of each VoIP client within the network topology is recorded in a central registry which acts like a “phone book” for the VoIP devices. This centralized registry is required by all state-of-the-art VoIP devices before VoIP communication between any of the devices may be established. This central registry is called the Session Initiation Protocol registry, or the “SIP” registry. Per a wikipedia.org article, “Session Initiation Protocol (SIP) is a signaling protocol, widely used for setting up and tearing down multimedia communication sessions such as voice and video calls over the Internet. Other feasible application examples include video conferencing, streaming multimedia distribution, instant messaging, presence information and online games. The protocol can be used for creating, modifying and terminating two-party (unicast) or multiparty (multicast) sessions consisting of one or several media streams. The modification can involve changing addresses or ports, inviting more participants, adding or deleting media streams, etc.”
Under the prior art, the SIP registry is located on a centralized server attached to the same network as any VoIP devices. If a client connected to a network node (the calling party) wishes to call another user (the receiving party) but the path between the calling party and the server containing the SIP server and SIP registry is broken, then the VoIP call is not possible with prior art network architectures. This is especially unfortunate if the network communications path between the calling party and the receiving party is still operational, but the sole lost connection is between the two parties and the SIP server. The loss of VoIP operation is especially vexing if the communication system is mission critical and lives or property are on the line. In these situations, a more versatile and reliable solution is needed.
The requirement of one or more centralized SIP servers are discussed in several prior art references. For example, a recently granted patent, U.S. Pat. No. 7,408,928 to Bradd, et. al., describes a method of overcoming the difficulties created by communication with one or more centralized SIP servers when the central SIP servers serve networks with conflicting address domains. Bradd teaches that the “the call servers also need to be reachable from the media gateways within their respective associated networks.” Col. 4, Lines 65-67.
The joining of networks containing VoIP devices is traditionally solved by the installation of an intermediary which directs traffic from one network and unto another network. For example, U.S. Pat. No. 7,443,842 to Takashi Miyamoto, discusses a central “control apparatus” which facilitates communication between IP devices in two different networks. The instant invention eliminates the need for a central control apparatus, as this prior art patent teaches.
Further prior art approaches rely on proxy servers. A proxy server is a type of intermediary service which forwards requests from clients to a server and any responses from a central server to clients. Proxy servers, contrary to this invention, nonetheless require a connection to a central server. While some proxy servers may cache requests and responses when communications with the central server are interrupted, an approach relying on proxy servers nonetheless requires one or more central servers. The instant invention facilitates communication in circumstances where a central server is consistently absent.
A mission critical situation involving wireless communication might include a group of first responders arriving on a scene where no backhaul connection is available or has yet to be established. Here, one network node may exist on a vehicle and other network nodes may exist as part of units carried by personnel on the scene. These nodes could form an isolated cluster. However, under the prior art, it is not possible to establish VoIP sessions between VoIP devices associated with each node comprising the isolated cluster until a SIP server is also connected to the isolated cluster. Other than first responders, soldiers in the field may encounter a similar scenario. Further, the isolated cluster may be initially in communication with a SIP server through a backhaul connection, but that backhaul connection is later lost due to movement of the network nodes or a failure of the backhaul communications link. A further scenario involving wired communications, or a combination of wired and wireless communications, could involve a campus network. Here, a building or group of buildings having a wired network infrastructure may act as an isolated cluster for VoIP communications within that cluster when the backhaul connection to a SIP server which is external to the building or group of buildings is no longer available.